title: Evolutionary reversals of antibiotic resistance in experimental populations of Pseudomonas aeruginosa.
abstract: Antibiotic resistance mutations are accompanied by a fitness cost, and two mechanisms allow bacteria to adapt to this cost once antibiotic use is halted. First, it is possible for resistance to revert; second, it is possible for bacteria to adapt to the cost of resistance by compensatory mutations. Unfortunately, reversion to antibiotic sensitivity is rare, but the underlying factors that prevent reversion remain obscure. Here, we directly study the evolutionary dynamics of reversion by experimentally mimicking reversion mutations-sensitives-in populations of rifampicin-resistant Pseudomonas aeruginosa. We show that, in our populations, most sensitives are lost due to genetic drift when they are rare. However, clonal interference from lineages carrying compensatory mutations causes a dramatic increase in the time to fixation of sensitives that escape genetic drift, and mutations surpassing the sensitives' fitness are capable of driving transiently common sensitive lineages to extinction. Crucially, we show that the constraints on reversion arising from clonal interference are determined by the potential for compensatory adaptation of the resistant population. Although the cost of resistance provides the incentive for reversion, our study demonstrates that both the cost of resistance and the intrinsic evolvability of resistant populations interact to determine the rate and likelihood of reversion.
authors.affiliation: Department of Zoology, University of Oxford, United Kingdom. danna.gifford@zoo.ox.ac.uk.
authors.forename: Danna R
authors.initials: DR
authors.lastname: Gifford
authors.forename: R Craig
authors.initials: RC
authors.lastname: MacLean
mesh_terms: D005075:Biological Evolution; D024881:Drug Resistance, Bacterial / Q000235:genetics*; D040961:Genetic Drift; D056084:Genetic Fitness / Q000235:genetics; D005828:Genetics, Population; D008957:Models, Genetic; D011550:Pseudomonas aeruginosa / Q000235:genetics*; D013045:Species Specificity
keywords: Compensatory evolution; evolvability; genetic drift; probability of fixation; rifampicin